It is known that the technique of the spirometric measuring, i.e. the analysis of the breathing functionality, always provides a tester of the inspired and expired air volume or of the speed or flux of the same. Usually, a device transforming the primary measuring obtained by the testing is transformed into an electric signal by a device provided downstream of the tester.
The most commonly used physical phenomena onto which the flux tester are based are two: the one exploiting the pressure determined at the passage of a fluid according to the Venturi principle, and the one that obtains the measuring of the air volume from the rotation of a turbine placed in between the flux.